Method of preparing linear



Patented Mar. 18, 1952 UNITED STATES PATENT OFFICE METHOD OF PREPARINGLINEAR POLYESTERS Paul J. Flory, Kent, and Frederick S. Leutner,Cuyahoga Falls, Ohio, assignors to Wingfoot Corporation, Akron, Ohio, acorporation of Delaware No Drawing. Application July 16, 1946,

. Serial No. 683,989

1 15 Claims. (01. 260-75) prepared by reversible reactions whereinmoderately volatile by-products, such as water, are evolved; forexample, polymeric ethylene succinate may be prepared by the prolongedheating together of ethylene glycol and succinic acid. It is well knownthat the formation of high molecular weight condensation productsrequires that the reaction'be carried very nearly to completion. In thepreparation ofpolyesters by reversible methods, it is necessary thateflicient methods for removal of the Water, or other byproduct, be used,in order that the condensation is not impeded by occurrence of thereverse reaction. Consequently the prior art is concerned with specialmethods for removing the by-products, for example, the use of amolecular still or other operations involving the use of low pressureswith inert gas bubbling through the molten polymer. Furthermore, whenthese comparatively slow reversible reactions are employed, undesirablylong reaction periods are required to achieve satisfactory molecularweight.

One purpose of this invention is toprovide a method for the preparationof certain polyesters by a non-reversible condensation reaction. Anotherpurpose of this invention is to prepare high molecular Weight polyestersin a much shorter period of time than is required by prior art methods.A further purpose of this invention is to prepare linear polyesters ofunusually high molecular weight.

These objects are accomplished by co-reacting one of a specific class ofglycols in a high state of purity with a pure diacid chloride of asuitable dibasic acid. The reaction between the glycol and the dibasicacid chloride may be indicated as follows:

This condensation reaction differs from those disclosed in the prior artby being non-reversible;

that is, the glycol and thedibasic acid chloride cannot be regeneratedby the action of hydrogen chloride on the polyesters. Furthermore, thecondensation is not impeded by the presence of the by-product, which inthis case is hydrogen chloride. However, it is usually desirable topermit rapid evolution of the hydrogen chloride during the reaction. Nospecial methods, such I as the maintenance of high vacuum or blowingwith inert gas for prolonged periods are required for the removal ofthis by-product, owing to its ready volatility.

One of the principal beneficial results achieved by the practice of thisinvention is the exceedingly rapid rate of reaction. Whereas it iscustomary to heat a dibasic acid with a glycol for a period of severaldays at a high temperature in order to reach a molecular weight which isadequate for the attainment of optimum physical properties, this methodmerely requires heating at moderate temperatures and for a few hours atmost, and often the polymerization isv substantially complete afterheating for less than one hour. Because of the low temperature requiredand the shortperiod of heating,the products are obtained in a colorlessor a very light colored condition, being substantially unaffected byoxidation and other undesirable side reactions. Because of the rapidityand the non-reversible nature of this reaction, linear polyesters ofexceptionally high molecular weights can be prepared. The method of thisinvention is not applicable to the preparation of superpolymers from allglycols, and polymers of the desired high molecu lar weight arenotobtained by the condensation of some glycols, for example, ethyleneglycol with dibasic acid chlorides. In particular, it has been foundthat any aliphatic or cycloaliphatic glycol in which the shortest chainbetween the hydroxy groupshas more than three atoms is useful. Theoperative glycols may be represented by the structural'iormula;

in which R may be any aliphatic divalent hydrocarbon, oxahydrocarbon, orthiahydrocarbon radical having at least four, atoms, which may includean oxygen or sulfur atom, as well as carbon atoms, in the aliphaticchain between the two valence bonds. Thus, suitable glycols which may beused in the practice of this invention are tetramethylene glycol,hexamethylene glycol, decamethylene glycol, diethyleneglycoL'triethylene glycol, 1,4-quinitol, tetraethylene glycol, 2,2-dihydroxy diethyl sulfide and 3,3-dihydroxy diof the polyesters arethose whichhave at least three atoms in the shortest atom chain betweenthe carbonyl groups and which have the carbonyl groups attached toaliphatic-carbon atoms. Thus, useful acid chlorides include those of thealiphatic hydrocarbon dicarboxylic acids, such a glutaryl chloride,adipyl chloride, sebacyl chloride, subaryl chloride and theacid'chlorides of pimelic acid, azelaic acid, brassylic acid andhomologues thereof, the araliphatic hydrocarbon dicarboxylic acidchlorides, such as the phenylene diacetic acid chlorides, phenylenedipropionic acid chlorides, naphthalene diacetic acid chlorides,naphthalene dipropionicacid-chlorides homologues thereofcontaining-longer aliphatic chains and other arylene radicals, theoxahydrocarbon dicarboxylic acid chlorides, such as the acid chloride ofdihydracylic acid; the acid chloride of diglycolic acid and homologuescontaining other aliphatic or araliphatic radicals containing etheroxygen substituents, and the thiahydrocarbon aliphatic dicarboxylic acidchlorides containing aliphatic or araliphatic radicals which have a thioether sulfur atom substituted therein, for example, thiodiglycolylchloride,

ClCOCHzSCI-IzCOCl According to the practice of the present invention,polyesters are prepared by mixing molecular equivalent quantities of theglycol and. the dibasic acid chloride. In some cases it is preferred toadd the glycol to the dibasic acid chloride in successive portions, orin small increments, at a rate, such that there is no appre ciableaccumulation of unreacted glycol. Usually it is sufilcient,-however,merely to mix the total reactants in a single step. Portionwise additionof dibasic acid chloride to the glycol usually is undesirable; thehydrogen chloride released by the mainreaction may react with theglycol, or induce it to etherify 'or to undergo other side reactions. Ifone or the other of the reactants is a solid at room temperature, it maybe necessary to warm' the mixture in order to effect complete solution;otherwise the reaction ordinarily begins at room temperature or slightlyabove with evolution of hydrogen chloride and a spontaneous rise intemperature. proceeds, the mixture in warmed gradually to a temperaturein the vicinity of 200 C. After maintaining the reaction mixture at thistemperature for a few .minutes,evolution of hydrostream of inert gas,such as oxygen-free nitrogenthrough the melt. Intermittent applicationof As the process 4. radative reactions and other side reactions whichcause discoloration of the polymer.

Ordinarily, it is desirable to employ reactants which are in a highstate of purity; they should be at least 98 percent pure and preferably99.5 percent or better. Otherwise, very high'molecular weight productscannot be secured. Similarly, it desirable to employ the reactants invery nearly molecularly equivalent proportions; preferably less than onepercent excess of either re- 'a'ctant is used. Exceptions occur when oneor the other reactant is lost by volatilization during thepolymerization. In this case an excess for the amount lost duringpolymerization.

It is true that certain impurities present in small amounts do notinterfere with the progress of the polymerization; for example, certainbifunctional impurities which co-react with the main reactants may notexert a deleterious infiuence when present in' small quantity. Certainother impurities, for example inert materials, can be compensated forbyemployingan appropriate excess of the slightly impure cc-reactant. Thegeneralizations in the preceding paragraph concerning the desirabilityof employing pure reactants have been drawn without consideration forthese exceptions. Usually the precise nature of the impurities presentin small amount is not definitely known. Consequently, it is soundpractice to specify high purity in the starting materials.

The extent of polymerization, or number average molecular Weight, can beestimated from a measurement of the viscosity of the molten polymer. Aconvenient method for measuring melt viscosity is described in theJournal of the American Chemical Society, 62, 1057 (1940)". The averagemolecular weight M is related to the melt viscosity according to theempirical equation log 1;=A+BM where '27 is the viscosity in poises, andA and B are constants. These constants can be established by measuringthe melt viscosities of polymers of known molecular weights. Polymers ofknown molecular weights can be prepared according to the processof. thepresent invention by co-reacting the dibasic acid chloride with apredetermined excess of the glycol. The molecular weights can then beestimated by calculations based on the amount of glycol employed inexcess of equivalency; equations given in the literature on condensationpolymers can be employed for this purpose (see J. Am. Chem. Soc., 56,1877(1936); J. Am. Chem. Soc, 62, 105'], 2255 (1940)). A and B, in theabove equation vary somewhat from one polyester to another, depending onthe particular pair of co-reactants employed. However, this variationgenerally is small, and consequently it is not always necessary toevaluate the constants for each polyester. Rough estimates of molecularweight can be made from the melt viscosity by employing the contactsknown to apply to an analogous polymer. i

The superpolymers prepared in accordance with this invention willgenerally have a melt V viscosity of over 25 poises at 200 C., or abovereduced pressure usually aids in the removal of bubbles from the viscousmass. The presence of traces of oxygen in contact with the polymer athigh temperature leads to undesirable deg if the melting point of thesuperpolymer exceeds 200 C. The preferred polymers will have meltviscosities in excess of 50 poises. Some of the products will have lowermelt viscosities.

Polyesters having molecular weights above about 10,000 are prepared withdifiiculty by prior art methods employing reversible condensationreactions. Only in a few cases have polymers;

The constants,

with molecular weights above 15,000 been prepared by these methods. Thenon-reversible acid chloride method on the other hand generally producespolymers having molecular weights above 15,000. Often the molecularweights exceed 25,000. b

The method of this invention may also be used to prepare condensationproducts from a plurality of the glycols and one of the acid chloridesof the dibasic acids, from one of the glycols and a plurality of theacid chlorides of dibasic acids, or from a mixture of two or moreglycols and two or more of the acid chlorides. These interpolymericcondensation products are usually more thermoplastic and lesscrystalline than those pre pared from a single glycol and a single acidchloride. The interpolymeric types are usually less desirable for thepreparation of filaments and fibers. As described above, theinterpolymeric types are usually and preferably prepared from purereagents used in equimolar proportions.

The polymers are frequently crystalline solids at room temperatures andhave melting points which depend upon the particular combination ofreactantsemployed. Some of the polymers, for example, those made fromthe polyethylene glycols, are usually viscous liquids at roomtemperatures and others are decidedly rubber-like. Generally, thepolymers can be converted to a liquid or non-crystalline state byheating.

The polyesters prepared in accordance with this invention are usefulcompositions for the preparation of fibers, sheets, and other moldedshapes. The compositions may be extruded in either the molten state, orin solution in suitable solvents through orifices or dies andsubsequently solidified by cooling, or in the case of solutions, bycontacting with a drying atmosphere or other means for removing thesolvent. The fibers which are prepared from the high molecular weightcompositions are capable of being cold drawn, which operation produces areduction in the extensibility and increases the tensile strength of thefilament. filaments are useful in the preparation of woven fabrics or asbristles in the manufacture of brushes. Smooth sheets or films of thepolymers may be prepared by casting the polymer solutions on smoothsurfaces, or by calendering the polymer between rollers, heating ifnecessary to soften the polymer. The interpolymeric condensationproducts are not useful in the preparation of filaments, but can be usedas coating compositions, films and as rubber substitutes. Generally, anyof the crystalline or non-crystalline types may be fabricated to formarticles of irregular shape by molding under the influence ofv heat andpressure.

Further details of the preparation of polyesters in accordance with thisinvention are set forth in the following examples.

Example 1 A closed glass reaction vessel was provided with a pipettetype of viscometer and was vented through a two-way valve to theatmosphere .or to a vacuum pump. The viscometer was adjustable so thatthe end thereof could be immersed in the polymer within the reactionvessel. The viscometer was also used to provide a slow stream ofoxygen-free nitrogen through the reaction flask during the course of thereaction. Equivalent weights of the reactants, 3.605 parts by weight ofdecamethylene glycol and 4.949 parts of sebacyl chloride, were placed inthe vessel and The tensilized 6 v heated for 5 minutes at 110 C. Thetemperature was then increased to 218 C. and within a few minutes a veryviscous polymer was obtained. After two hours a vacuum of 10 mm. totalpressure was applied for about 5 minutes to remove gas bubblesconsisting of hydrogen chloride gas. At the end of two hours the polymerwas found to have a viscosity of 6900 poises and at the end of fourhours a viscosity of 14,500 poises. The elapsed time of reactionrequired to produce these viscous polymers is probably longer than wouldbe required since it was necessary to allow the highly viscous polymerto flow to a compact mass at the bottom of the vessel before viscositymeasurements could be made properly.

For comparison with the above reaction, 9.193 parts by weight of sebacicacid and 8.018 parts of decamethylene glycol (1.012 molecularequivalents) were placed in a similar reaction vessel. After heating onehour at 176 C. while bubbling nitrogen through the melt, the temperaturewas raised to 218 C. and heated at this temperature until a viscosityapproximately equal to that obtained from the above-describedpreparation involving sebacyl chloride was reached. The viscosities weremeasured at -convenie'nt intervals and are set forth in the followingtable.

The above tabulated data demonstrate that the reaction involving the useof the acid chloride is very much faster than the corresponding reactioninvolving the corresponding acid. In addition, the polymer prepared fromthe acid chloride was a white crystalline solid, whereas the polyesterprepared from the acid was. quite dark in color and contained somegelatinous matter. The

composition prepared in accordance with the prior art method was notentirely thermoplastic. The composition prepared from the acid chloridewas capable of being extruded into filaments which could be cold drawninto strong resilient Example 2 Using the apparatus and proceduredescribed in- Example 1, 5.608 parts by weight of decamethyl ene glycoland 5.89 parts (one equivalentl'of freshly distilled adipyl chloridewere co-reacted.- The reactants were heated at C. in a slow. stream ofpure nitrogen for about 10 minutes andthen at 218 C. for 1 hours. Theresulting;

" polymer had a viscosity of 6800 poises at 218C.

and solidified to a white crystalline material at room temperature whichcould be drawn into fibers capable of being cold drawn with anincident'increase in tensile strength.

To demonstrate the critical nature of the stipulation relating to theacid chlorides which may be employed successfully, a control was run inwhich succinyl chloride was substituted for the adipyl chloride. In thispreparation, which was conducted identically to that described above,6.629 parts of decamethylene glycol and 6.003 parts (1.01 equivalent) ofpure succinyl chloride were reacted in a slow stream of pure nitrogenwhile gradually increasing the temperature from 110 C.-to 218 C. over aperiod of about 8 /2 hours. At this time a melt viscosity of 1.9 poiseswas measured. The product was a white solid at room temperature butcould not be drawn into fibers.

Example 3 1 Using an apparatus identical to that used in Example 1, anda similar procedure, 7 .061 parts of sebacyl chloride and 3.151 parts(1.005 equivalent) of diethylene glycol were placed in the reactionvessel at a temperature below 25 C. The reaction temperature was thenincreased to 110 C. and maintained thereat for one-half hour, afterwhich the temperature was increased to 218 C. which was maintained forone hour and 15 minutes. At the end of this time the melt viscosity was92 poises. The polyester so formed was a white translucent solidsoftening at a temperature of 35 to 38 C.

Although the invention has been defined with respect to specificexamples, it is not intended that the details thereof shall be construedas limitations upon the scope of the invention except to the extentincorporated in the following claims.

We claimz' H 1. A method of preparing. a superpolyester which consistsof forming a mixture in which the sole reactants are equimolecularproportions of (A) a glycol in which the shortest atom chain between thetwo hydroxyl groups contains at least four atoms and which has thestructural formula:

in which R is a divalent radical of the group consisting ofcycloaliphatic hydrocarbon, aliphatic hydrocarbon, aliphaticoxahydrocarben and aliphatic thiahydrocarbon radicals and (B) an acidchloride having the molecular structure in which R is any divalentradical of the group consisting of hydrocarbon, thiahydrocarbon, andoxahydrocarbon radicals, in which the shortest chain between thecarbonyl groups contains at least three atoms, and in which the carbonylgroups are attached to aliphatic carbon atoms, and heating the mixtureuntil the resultant polyesterv has attained a number average molecularweight of at least 10,000.

2. The method defined by claim 1 in which the heating and mixing areperformed simultaneously.

3. A method of preparing superpolyesters which consisted formingamixture in which the sole reactants are equimolecular proportions of analiphatic glycol in which there is a hydrocarbon chain of at least fourcarbon atoms between the two hydroxylgroups, said glycol containing onlycarbon-and hydrogen atoms, except for the 1131-:

droxyl oxygen, and an acid chloride having the structural formula:

in which R is any divalent hydrocarbon radical, and heating said mixtureuntil the resultant polyester has attained a number average molecularweight of at least 10,000.

4. The method defined by claim 3 in which the heating and mixing areperformed simultaneously.

, 5. A method of preparing superpolyes'ters which consists of forming amixture in which the sole reactants are equimolecular proportions ofdecamethylene glycol and sebacyl chloride, and heating said mixtureuntil the resultant polyester has attained a number average molecularweight of at least 10,000.

6. The method defined by claim 5 in which the mixing and heating areperformed simultaneously. v

'7. A method of preparing superpolyesters which consists of forming amixture in which the sole reactants are equimolecular' proportions ofdecarnethylene glycol and adipyl chloride, and heating said mixtureuntil the resultant polyester has attained a number average molecularweight of at least 10,000.

8. Themethod defined by claim '7 in which the mixing and heating areperformed simultaneously.

9. A method of preparing superpolyesters which consists of forming amixture in which the sole reactants are equirnolecular proportions ofdiethylene glycol and sebacyl chloride, and heating said mixture untilthe resultant polyester has attained a number average molecularweight ofat least 10,000.

10. The method defined by claim 9 in which the mixing and heating areperformed simultaneously.

11. A method of preparing a superpolyester which consists of forming amixture in which the sole reactants are equimolecular proportions of (A)at least one glycol in which the shortest atom chain between the twohydroxyl groups contains at least four atoms and which has thestructural formula:

in which R is a divalent radical of the group consisting ofcycloaliphatic hydrocarbon, aliphatic hydrocarbon, aliphaticoxahyclrocar-bon and a1i-' phatic thiahydrccarbon radicals and (B) atleast one acid chloride having the molecular structure ester hasattained'a number average molecular,

weight of at least 10,000.

12. A method of preparing a superpolyester which consists of'forming amixture in which the sole reactants are equimolecular proportions of (A)at least one glycol in which the shortest atom chain between the twohydroxyl groups contains at least four' atoms and whichhas thestructural formula:

' in which R is a divalent radical of the group consisting ofcycloaliphatic hydrocarbon, aliphatic hydrocarbon, aliphaticoxahydrocarbon and aliphatic thiahydrocarbon radicalsgand (B) at leastone acid chloride having the molecular structure 0 (ll-(l-E-Jl-Cl inwhich R is any divalent radical of the group consisting of hydrocarbon,thiahydrocarbon, and oxahydrocarbon radicals, in which the shortestchain between the carbonyl groups contains at least three atoms, and inwhich the carbonyl groups are attached to aliphatic carbon atoms, andheating the mixture until the+resultant polyester has attained a numberaverage molecular weight of at least 15,000.

13. A method'of preparing a'superpolyester which consists of forming amixture in which the sole reactants are equimolecular' proportions of(A) at least one glycol in which the shortest atom chain between the twohydroxyl groups contains at least four atoms and which has thestructural formula:

in which R is a divalent radical of the group consisting ofcycloaliphatic hydrocarbon, aliphatic hydrocarbon, aliphaticoxahydroclarbon and aliphatic thiahydrocarbon radicals and (B) at leastone acid chloride having the molecular structure in which R is anydivalent radical of the group consisting of hydrocarbon,thiahy'clrocarbon, and oxahydrocarbon radicals, in which the shortestREFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,012,267 Carothers Aug. 27, 19352,094,608 Kritchevsky Oct. 5, 1937 2,224,037 Brubaker et al Dec. 3, 19402,314,972 Dreyfus Mar. 30, 1943 2,437,046 Rothrock et al Mar. 2, 19482,465,150 Dickson Mar. 22, 1949 2,465,319 Whinfield et al. Mar. 22, 1949FOREIGN PATENTS Number Country Date 63,874 Denmark Aug. 27, 1945 OTHERREFERENCES I Wertheim, Textbook of Organic Chemistry (page 193), 2ndedition, 1945, published by Blakiston Co., Philadelphia, Pa,

1. A METHOD OF PREPARING A SUPER POLYESTER WHICH CONSISTS OF FORMING AMIXTURE IN WHICH THE SOLE REACTANTS ARE EQUIMOLECULAR PROPORTIONS OF (A)A GLYCOL IN WHICH THE SHORTEST ATOM CHAIN BETWEEN THE TWO HYDROXYLGROUPS CONTAINS AT LEAST FOUR ATOMS AND WHICH HAS THE STRUCTURALFORMULA: